Metal-oxide-semiconductor (MOS) capacitors with sputtering-deposited Gd-doped HfO2(HGO) high k gate dielectric thin films and ALD-derived Al2O3 interfacial passivation layer were fabricated on GaAs substrates. The effects of the passivation layer and the forming gas annealing (FGA) temperature were explored by studying the interfacial chemical bonding states and electrical properties of HGO/GaAs and HGO/Al2O3/GaAs gate stacks via x-ray photoelectron spectroscopy (XPS), capacitance-voltage (C–V), and leakage current density-voltage ( J–V) measurements. Results indicated that the MOS capacitors performances were enhanced by performing FGA. The electrical analysis revealed that the 300 °C-annealed Al/HGO/GaAs/Al MOS capacitor with 20 cycles Al2O3 passivation layer experienced improved electrical properties, with a dielectric constant of 44, a flat band voltage of 0.64 V, a hysteresis of 0.02 V corresponding to the oxide charge density of −6.2 × 1012 cm2, border trapped oxide charge density of −3.02 × 1011 cm2, a leakage current density 5.87 × 10-6 A/cm2 at a bias voltage of 2 V. The low temperature (77–300 K) dependent detailed current conduction mechanisms (CCMs) of the 300 °C-annealed MOS capacitor at low temperatures were also systematically investigated. The optimized interface chemistry and the excellent electrical properties suggested that HGO/Al2O3/GaAs potential gate stacks could be applied in future III-V-based MOSFET devices.

Interface Modulation and Optimization of Electrical Properties of HfGdO/GaAs Gate Stacks by ALD-Derived Al2O3 Passivation Layer and Forming Gas Annealing

Surfaces of semiconductors are notorious for the presence of electronic defects such that passivation approaches are required for optimal performance of (opto)electronic devices For Ge, thin films of Al2O3 prepared by atomic layer deposition (ALD) can induce surface passivation; however, no extensive study on the effect of the Al2O3 process parameters has been reported In this work we have investigated the influence of the Al2O3 thickness (1–44 nm), substrate temperature (50–350 °C), and post-deposition anneal (in N2, up to 600 °C) We demonstrated that an effective surface recombination velocity as low as 170 cm s−1 can be achieved The role of the GeOx interlayer as well as the presence of interface charges was addressed and a fixed charge density $${Q}_{\mathrm{f}}=$$
 −(18 ± 05) × 1012 cm−2 has been found The similarities and differences between the passivation of Ge and Si surfaces by ALD Al2O3 prepared under the same conditions are discussed

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Surface passivation of germanium by atomic layer deposited Al2O3 nanolayers

Nonvolatile memory capacitors based on Al2O3 tunneling and HfO2 blocking layers with charge storage in atomic-layer-deposited Pt nanocrystals

Surface treatment for Ge substrates using hydrogen chlorine cleaning and chemical passivation are investigated on AuTi/Al2O3/Ge metal-oxide-semiconductor capacitors. After hydrogen chlorine cleaning, a smooth Ge surface almost free from native oxide is demonstrated by atomic force microscopy and x-ray photoelectron spectroscopy observations. Passivation using a hydrogen chlorine solution is found to form a chlorine-terminated surface, while aqueous ammonium sulfide pretreatment results in a surface terminated by Ge-S bonding. Compared with chlorine-passivated samples, the sulfur-passivated ones show less frequency dispersion and better thermal stability based on capacitance-voltage characterizations. The samples with HCl pre-cleaning and (NH4)2S passivation show less frequency dispersion than the HF pre-cleaning and (NH4)2S passivated ones. The surface treatment process using hydrogen chlorine cleaning followed by aqueous ammonium sulfide passivation demonstrates a promising way to improve gate dielectric/Ge interface quality.

https://iopscience.iop.org/article/10.1088/0256-307X/29/4/046801/pdf

The Impact of HCl Precleaning and Sulfur Passivation on the Al 2 O 3 /Ge Interface in Ge Metal-Oxide-Semiconductor Capacitors

The high temperature thermal stability of ultra-thin atomic layer deposited Al2O3 on sulphur passivated and hydrofluoric acid (HF) treated germanium surfaces was studied using soft x-ray photoemission spectroscopy. The interface sulphur component was stable up to 500 °C vacuum annealing. The interfacial oxides were completely removed at 600 °C for the sulphur passivated sample, whereas HF treated sample showed traces of residual oxides at the interface. However, this annealing treatment does not show any significant change in Al2O3 stoichiometry. The dielectric-semiconductor band offsets were estimated using photoemission spectroscopy measurements.

Xiaochun Chen

Papers

Effect of chemical surface treatments on interfacial and electrical characteristics of atomic-layer-deposited Al2O3 films on Ge substrates